It is known that the working spindle of a lathe, for example, can be mounted in the area of the hub of the spindle in roller bearings with ball-cylinder rollers, in roller bearings with tapered rollers, in friction bearings, in hydrostatic bearings or hydrodynamic bearings. Conventional angular contact ball bearings are supplied by the manufacturer with different levels of prestress. Normally bearings with a low prestress are used. In order to achieve optimum conditions with regard to the prestress required in use of double row cylinder bearings with a tapered bore, it is also known that the taper on the main spindle can be designed with a positive slope in order to impart a different prestress to the rows of cylindrical rollers. However, this requires a suitable corresponding design of the bearing bore.
The reason why certain prestress conditions are desired is the fact that the cantilever length of the spindle, i.e., the lever arm which acts on a certain bearing and is the determining factor for the bowing of the spindle, should be as short and defined as possible.
With a conventional working spindle bearing with angular contact ball bearings in tandem O arrangement, this cantilever length cannot be defined precisely in many cases because it is impossible to assure that the outer bearing has the greatest prestress and thus also the greatest rigidity. This cantilever length enters the calculation of rigidity with the third power and can extend into the middle bearing if the prestress of the individual bearings is not defined with sufficient accuracy, and this has negative effects on the efficiency and accuracy of the entire bearing assembly. This disadvantage appears especially when the workpiece to be machined is held only in a chuck without additional support.
In order to have the shortest possible cantilever length, it is already known (German Patent No. 3,233,914) that the bottom of a chuck to be mounted on the spindle flange can be integrated into this flange and thus the effective cantilever length is shortened. However, the the bearing application cannot be improved by this measure.